ULTRASTRUCTURAL AND ELECTRON-ENERGY-LOSS SPECTROSCOPY STUDIES OF SEQUESTRATION MECHANISMS OF CD AND CU IN THE MARINE DIATOM SKELETONEMA-COSTATUM

The marine diatom Skeletonema costatum was used to study mechanisms of detoxification when submitted to cadmium and copper contamination. Af ter 96 h of growth, concentration corresponding to 50% growth inhibiti on (IC50, 96 h) was 0.224 mg/L for cadmium and 0.045 mg/L for copper, indicating that copper is more toxic for S. costatum than cadmium. Hea vy cellular damages were observed for cadmium and copper concentration s close to the IC50. Exposure to these concentrations induced a migrat ion of inclusions from the peripheral cytoplasm to the vacuole. Electr on energy loss spectroscopy (EELS) investigations demonstrated that Cd and Cu were specifically trapped in these inclusions. However, Cu was less sequestered than cadmium in the vacuole. EELS determination of o xidation states evidenced that trace metals were sequestered as Cd2+ a nd Cu2+. Nitrogen and sulfur are involved in metallic storage, especia lly in the case of cadmium contamination.